Method for producing and recovering aromatic hydrocarbons



Oct. 9, 1956 c. H. wATKlNs 2,766,305

METHOD FOR PRODUCING AND RECOVERING AROMATIC HYDROCARBONS Filed March 2l. 1952 Unite States Patent METHOD FOR PRODUCING AND RECOVERING AROMATIC HYDROCARBONS Charles H. Watkins, Western Springs, Ill.,

Universal Oil Products poration of Delaware assigner to Company, Chicago, Ill., a cor- This invention relates to an improved method for effecting ahigh production of aromatic hydrocarbons and recovering the latter. More specifically, the present improvement is directed to a combined operation which provides for commingling :an 'aromatic :rich hydrocarbon stream with a high temperature oleflnic stream in 2a manner effecting 'the cracking of non-aromatic material in the aromatic rich stream and the conversion of yat least a portion of the olenic hydrocarbons to form additional aromatics in a substantially pure form permitting the fractional separation thereof.

In view of the present shortage of 'benzene and other aromatic hydrocarbons, it has been necessary to supply these critical materials from petroleum. However, one of the present problems in connection with the production and recovery of aromatic's, such as benzene, toluene 'and the like from certain of the petroleum processing operations is that they can not be recovered by distillation to provide desired purities. kFor example, there are various desirable catalytic reforming operations which can be utilized to provide high yields of aromatic hydrocarbons, but the aromatics tend to form azeotropes with the resulting non-aromatic hydrocarbons and the separation of the aromatics in desired purities by distillation in order to provide industrial or nitration grade products is substantially impossible. 'Certain solvent extraction operations may be util-ized to selectively separate the aromatics and provide the desired purities; however, the use of solvents may be expensive and troublesome, aswell as require considerable contacting equipment in addition to fracti-onating apparatus.

It is, therefore, a principal object of the present invention to provide a desirable method for converting nonaromatic hydrocarbons in lan aromatic rich stream so that there is a minimum of azeotrope formation, whereby fractional separation of the aromatics may be carried out satisfactorily.

It is also an object of the present invention to provide a method for commingling 'an aromatic rich stream with a high temperature cracked stream, particularly one high in ethylene land propylene, which can be converted to aromatics, while heating, cracking and substantially converting non-aromatic hydrocarbons into additional low molecular weight olens, which in turn may be converted to provide still further quantities of aromatics.

A still further object of the invention is to effect the autothermic cracking of 'a low molecular weight parafnic `stream to provide a high temperature ole-finie stream suitable for commingling with 1an aromatic rich stream and in turn effecting the conversion of the non-aromatic hydrocarbons of the latter into olenic hydrocarbons which may provide the formation of additional aromatics.

Ina broad aspect, the present invention provides a method for producing and recovering a high yield of aromatic hydrocarbons from :an aromatic rich hydrocarbon stream in a manner which comprises, passing a cracked olefin containing hydrocarbon stream at a temperature in the range of from about 1400 F. to about 1600 F.

into contact with the aromatic rich stream and exothermically converting olefinic materials to form aromatic hydrocarbons while cracking non-aromatic components in the aromatic rich stream to form low molecular weight olelins and additional .aromatic hydrocarbons, recovering a substantially aromatic hydrocarbon stream and subjecting it to fractional distillation to effect the production of desired substantially pure aromatic fractions..

` The olenic stream preferably comprises a high quantity of low molecular weight olefins such as ethylene and propylene which may react at high temperatures to form desired aromatic hydrocarbon fractions such as benzene, toluene, etc. The olefin containing stream may be supplied frorn any source, such as a portion of a thermally or catalytically cracked stream; however, in one desirable operati-on, low molecular weight paraflinic hydrocarbons, such as ethane, propane, or other normally gaseous hydrocarbons other than methane, as Well as natural gas, all of which usually may be `obtained economically, provide desirable parafn hydrocarbons which 4in turn may be autothermically cracked to produce an olenic stream.

Thus, in a more specific embodiment of `the invention, suitable for producing and recovering a high yield of aromatic hydrocarbons, a normally gaseous paraiiinic hydrocarbon is passed into admixture with a stream of controlled oxygen content and there is effected the oxidative cracking -of said paraiinic stream to provide low molecular weight olenic hydrocarbons, subsequently introducing an aromatic rich hydrocarbon stream into contact with said resulting olefinic oxidatively cracked stream and effecting the thermal conversion of a major portion of the non-aromatic hydrocarbons of said aromatic rich stream to provide additional low molecular Weight hydrocarbons while simultaneously converting resulting olens present to form additional aromatic hydrocarbons, withdrawing and subjecting a resulting substantially aromatic hydrocarbon stream to fractional Vdistillation and recover` ing substantially pure aromatic fractions.

Preferably, the conversion of olens to aromatic hydrocarbons is carried out in the temperature range of from about l400 F. to about 1600 F. However, since the formati-on of -aromatics from the low molecular weigh-t oletins is an exothermic reaction, the resultant temperature m-ay exceed ()D F.; therefore, it is desirable to effect a cont-rolled temperature within the aromatic forming zone. Preferably, this may be accomplished by introducing an aromatic rich stream linto -admiXture with the resulting oxidatively cracked stream in incremental portions and at spaced points along the line of flow of the cracked stream as it passes through a suitable soaking chamber or through an .aromatic conversion zone. -I11 Iother words, by introducing aromatic rich stream at a tempera-ture which is something less than 160()D F. in stepwise increments, the temperature may be controlled in the conversion zone to prevent it from becoming excessive. IIn View of the fact that the aromatic formation from olefin requires rela-tively long periods of contacting, it is desirable to provide an elongated soaking chamber for passing the admixture of the olen stream and the aro/matic rich stream. Alternatively, it may be desirable to provide a series of two or more soaking chambers, or aromatic formation chambers, through which the mixed stream may pass, and into which the aromatic rich stream may be introduced by increments.

Where it is desired to obtain high yields of aromatics, it is necessary that the contact or residence time in the conversion zone or zones be sufficient `to appreciably reduce the olen content of the autothermically cracked stream. Also, it is preferable that the ethylene content in -the stream leaving less than about 12 weight percent of the total (22+ hydrothe aromatization zone should be n vll) carbons that are charged to the zone. lf the charge to the aromatization zone comprises an olein other than ethylene, substantially all of the olefin undergoes conversion to ethylene, aromatics, and parafns. Hence, ethylene is the only olen that Lappears in the aromatization zone efiiuent in signicant concentrations, and for this reason ethyle-ne concentration may be utilized as an operating control, regardless of the particular `olefin or Oleus charged to the yaromatization zone.

As previously noted, it is desirable to provide the cracked olein containing stream by the :oxidative or autothermic cracking of hydrocarbon heavier than ethylene. For example, ethane or any non-aromatic hydrocarbon containing at least 2 carbon atoms per molecule may be preheated and intimately mixed with a preheated air or oxygen containing stream having greater than about 20% oxygen by volume and allowing the same to react. The amount of oxygen relative to the -amount of hydrocarbon is preferably in an amount sutcient to bring about the conversion of atleast 90% of the paraflinic charge stream, since it has been found `that conversions of at least about 90% to low molecular weight oleins is essential to prepare an olelinic hydrocarbon stream which will in turn provide a desired exothermicity upon subsequent admixture with the aromatic rich stream in the aromatization zone.

The pressure for electing the cracking of nonarom'atic hydrocarbons and the formation of additional aromatics by contacting a high temperature olefin containing stream with the aromatic rich stream may be in the range of from about to 400 p. s. i. g. At pressures above 400 p. s. i. g., there may be considerable effect from undesirable side reactions. At pressures below `about 75 p. s. i. g., there is little trouble with carbon formation, Ior methane formation, while above l0() p. s. i. g., there may be 'an increase in the formation of these undesired products, and further, it is generally desirable to operate in the range of from V0 to 50 p. s. i. g. ln any case, from the standpoint of obtaining maximum yield and reducing side reactions, it is preferable to operate below about 400 p. s. i. g. However, since the space velocity in the aromatic formation zone may be increased with increasing pressures, and the resulting size of an aromatizing or soaking chamber, or chambers, may be proportionately decreased with increased pressures, it may in slome instances be desirable to utilize higher pressures, say within ythe range of from 100 to 400 p. s. i. g.

Reference to the yaccompanying drawing and the following description thereof will 'aid in clarifying the operation of one embodiment of the invention, and point out additional advantageous features in connection therewith.

Ethane or a stream of low molecular weight paraflinic hydrocarbons is passed by way of line 1 and valve 2 through "a suitable heater 3 and subsequently through line 4 to a mixing zone 5, while at the same time air or other oxygen containing stream is introduced by way of line 6, valve 7, to a heater S and then passed from the latter through line 9 into mixer 5. Each of these'streams are preferably heated or perheated to ya relatively high temperature say of the iorder of l000 l?. or more, so that they will spontaneously interact by partial combustion in :the mixing zone 5. The mixer is internally designed to provide rapid intimate mixing of the two streams *and the discharge thereof directly into a reaction zone 10, whereby there is oxidative cracking of ya portion of ythe hydrocarbon charge stream. in the mixing and reaction zones, there is partial combustion of a portion of the hydrocarbon stream to yield carbon oxides, hydrogen-fand some water, while the resulting high temperature products elect the thermal cracking and decomposition of a substantial portion of the remaining hydrocarbon stream to provide principally ethylene and minor amounts of other gases.

The reaction zone 10 is preferably insulated and internally linedto provide a substantially adiabatic reaction zone. This reaction zone may also have battles or a suitable packing material, such as Raschig rings, so that there is continued intermixing of the combustion gases and the hydrocarbon stream and resulting decomposition products. As hereinbefore noted, it is preferable to effect the oxidative cracking in a manner providing combustion reactions and cracking reactions that eect a conversion of the ethane and heavier hydrocarbons in the charge stream.

Normally, the preheating of the charge streams and the quantity of oxygen with respect to the quanti-ty of ethane or other hydrocarbon is such 'as to provi-de `a maximum cracking temperature in the range of from about l600 F. tto about 2000 F.

The resulting olenic hydrocarbon stream from the reactor 10 is passed directly from reactor chamber 10 into an elongated cracking and aromatizing chamber 11 at a resulting conversion `temperature and without substantial loss of heat. Chamber 1l in effect provides a soaking chamber for the formation of aromatics as well as ya cracking chamber for the conversion of non-aromatic hydrocarbons which are introduced thereto. in the present embodiment, the aromatic rich stream which is to undergo further conversion and arcmatization in accordance with the present invention, is passed by way of line 12, valve 13 and heater 14 into a distributing line 15. From. the latter, divided portions of the aromatic stream may be introduced stagewise into the cracking and soaking chamber 11. The heater 14 is utilized to preheat and raise the temperature of the aromatic rich stream to an economically desirable level, say of .the order of from about ll00 F. to about l200 F. In any case, the temperature of this Stream Will be les-s than about 1600 F. so as to prevent the oonversion temperature within chamber 11 from becoming excessively high as the exothermic reaction proceeds. A portion of the aromatic rich stream passes from distributing line 15 through line 16 and valve 17 into a first portion of the cracking and aromatizing chamber 11 and therein becomes admixed with the `oxidatively cracked olefnic stream from reactor 10 so that there is `a resulting cracking of non-aromatic hydrocarbons in `the intro-duced stream and the conversion of oletins into benzene and other aromatics. It is also to be noted rthat `the non-aromatic hydrocarbon components of the aromatic rich stream, which are introduced by way of lines 15 and 16 will be converted to ethylene and other low molecular weight olenic hydrocarbons so `that they vare thusly present to provide for the further production of aromatic hydrocarbons.

Since the aromatic formation reaction is exothermic, the temperature within the contacting chamber 11 tends to increase above the desired level, say of the order of l600 F., and it is therefore desirable to control and maintain this temperature below that level. In the present embodiment, a second portion of the aromatic rich charge stream passes by Way of aline 18 and valve 19 from header line 1S, and the resulting mixture Within the chamber is thus partially quenched and maintained below an excessively high temperature level. Similarly, a third portion of the aromatic rich stream passes by way of line 20 and valve 21 into the chamber 11 at a successive point along the line of flow of the oletinic hydrocarbon stream. Thus, by the introduction of incremental portions of the aromatic rich stream into contact with the resulting olefinic hydrocarbon stream at spaced points along its line of flow, the exothermic reaction temperature may be successively reduced and maintained within the desired conversion range.

The chamber 11 is also preferably internally refractory lined, in a manner similar to that of chamber 10 so that there is an iron free surface and so that there is a minimum of heat loss from the conversion zone with optimum conversions to the desired aromatic fractions. While the present embodiment indicates a single long aromatization chamber il, it is to be noted, that two or more substantially separate or individually lined conversion chambers may be placed in series in lieu of the single chamber. In which case, the aromatic rich stream would be introduced by increments into admixture with the resulting oleinic stream at the inlet of each of the conversion chambers.

The resulting substantially aromatic stream being withdrawn from the end of chamber 11 passes by way of line 22 and valve 23 to a suitable quenching and separating chamber 24. It is desirable in this zone toeifect the separation of heavy asphaltic-like aromatic oils from the product stream prior to passing it through the various fractionating zones. Thus, in the present embodiment, a relatively heavy quenching oil such as naphthalene, or a material heavier than xylene may be introduced through line 2S into the upper portion of the quenching and separating chamber 24 to effect the cooling of the product stream and to permit the recovery of the undesired heavy asphalt-like oils from the lower portion of the column 24. These oils are withdrawn by way of line 26 and valve Z7, while the lower boiling cut containing naphthalene and lighter aromatic materials is discharged overhead through line 28 and valve 29. Preferably, the cooling effected in the separating chamber 24 is such that the materials being withdrawn are at a temperature say of the order of about 60G-700 F. It is to be noted, that a temperature of 500 F. or lower may permit condensation of some of the naphthalene or more valuable aromatics. Thus, the lower boiling and more valuable aromatic products are introduced into the lower portion of an absorber column 30 by way of line 28 and valve 29. Subsequently, the aromatic fractions in column 30 are contacted by a suitable absorption oil, which may for example be a G-400 F. aromatic cut, containing toluene and heavier aromatics. This cut is introduced by way of line 31 and a suitable distributing header 32. A gaseous stream, high in ,olefin content, is discharged from the upper end of the absorber column by way of line 33 and Valve 34 while from the lower end of the column, the desired aromatics are withdrawn by way of line 35 and valve 36 for subsequent introduction into a benzene separating column 37. As diagrammatically indicated, .the benzene column 37 effects the overhead discharge of a substantially pure benzene aromatic fraction by way of line 38 and valve 39, while a stream containing toluene, xylene, and heavier aromatics is discharged by way of line 40 and valve 4l. A portion of this heavier cut, as indicated, may be withdrawn from line 40 by way of line 3l and control valve 42. Thus, a regulated quantity of absorbing oil may be passed to column 30. Still another line 43 having valve 44 is indicated diagrammatically as connecting with line 31, and is suitable to permit the introduction of a dilferent absorbing oil into column 30, where such oil is to be supplied from a source other than from the bottoms of benzene column 37.

The bottoms stream from column 37 is introduced into a toluene fractionation column 45, from which an over head toluene fraction is discharged by way of line 4d and valve 47. While from the lower end of column 45, by way of line 48 and valve 49, there is discharged the aromatic bottoms stream containing xylene, naphthalene and heavier desired materials. The aromatics from line 4S are subsequently introduced into a xylene fractionating column 50, from which is discharged an overhead xylcne fraction by way of line 51 and valve 52. The heavier aromatic oils from column are discharged by way of line 53 and valve 54 and may, if desired, undergo further separation and fractionation to recover naphthalene, etc. The present embodiment also indicates a portion of the heavier aromatic oils from the bottom of the xylene column 50 as passing by way of line S3 and line 25, having valve 5S, to provide the quenching oil that is introduced into the upper portion of the quenching and separating chamber 24.

Since, in accordance with the present invention, the

non-aromatic hydrocarbons contained inthe' aromatic` little formation of azeotropes between the non-aromatic hydrocarbons and the aromatic hydrocarbons, and that the separation effected in the various fractionating columns 37, 45 and 50 may be carried out to effect the recovery of substantially pure aromatic fractions, which may normally meet industrial or nitration-grade requirements.

It is also to be noted that the present embodiment does not limit the origin of the aromatic rich `charge stream `which undergoes further conversion to aromatics by contact with the oxidatively cracked oleiinic stream. In other words, the aromatic rich stream may be the product stream from a thermal or catalytic reforming unit, a dehydrogenation unit and the like, or other source providing a hydrocarbon stream with a high degree of aromatic components. It may, for example, be advantageous to pre-fractionate a` natural gasoline stream to separate C4 and lighter normally paramnic hydrocarbons as an overhead stream and charge them to the mixer 5 of the autothermic or oxidative cracking section of the present embodiment, while the C5 and heavier components of the fractionated natural gasoline stream may be passed to a catalytic reforming zone and therein contact suitable aromatizing catalysts so that there is a resulting reformed gasoline stream producing an aromatic rich stream. This latter stream may then be introduced, by way of line l2, into the cracking and aromatizing zone 1li for further conversion of the non-aromatic hydrocarbons in accordance with the embodiment of the present invention.

I claim as my invention:

l. A method for producing and recovering a high yield of aromatic hydrocarbons, which comprises, passing a normally gaseous paralhnic hydrocarbon stream into admixture with a stream of controlled oxygen content and eit'ecting the oxidative cracking of said gaseous hydrocarbon stream to provide a low molecular weight olefin-ic hydrocarbons at a temperature in the range of from about 1400" F. to abou-t l600 F., passing the resulting oleiinic hydrocarbon stream at the aforesaid resulting temperature into a conned cracking and aromatlization zone at a pressure bel-ow about 400 p. s. i. g. and commingling with said product stream an aromatic rich hyd-rocarbon stream, the latter stream being introduced into said conversion zone and 1into admixture with said oxidatively cracked stream in incremental portions along the line of flow of the latter in said zone, and with said aromatic rich stream being introduced into said. conversion zone at a temperature of less than 1600 F. and thereby controlling exothermic aromatics forming reactions to effect the thermal conversion of a major portion of the non-aromatic components of said aromatic rich stream into additional oletins and aromatic hydrocarbons while simultaneously converting resulting olefnic components from said oxidatively cracked stream into additional aromatic hydrocarbons, withdrawing a resulting substantially aromatic hydrocarbon stream from said zone and subject-ing it to cooling and fractional distillation and recovering desired substantially pure aromatic fractions.

2. A method for producing and recovering a high yield of aromatic hydrocarbons, which comprises, passing a normally gaseous paraflnic stream into admixture with a stream of controlled oxygen content and eifect-ing the oxidative cracking of said hydrocarbon stream providing a low molecular weight oleiinic hydrocarbon stream at a temperature within the range of from about 1400" F. to abou-t 1600" F., passing the resulting olefinic hydrocarbon stream at the aforesaid resulting temperature into a confined cracking and aromatizing zone at a pressure of less than about 400 p. s. i. g. and commingling with said oleiinic stream an aromatic rich hydrocarbon stream, intnoducing the latter stream into said cracking and aromatiz'ing zone in incremental portions along the line of ow ofthe oxidatively cracked olefinic stream, eecting the mixture of the incremental portion of said aromatic rich hydrocarbon stream With said oleiinic stream in a manner providing the thermal conversion of a major portion of the non-anomatic components of said aromatic nich stream into additional olelinic and aromatic hydrocarbons While simultaneously converting resulting olenic components fnom said oxidatively cracked stream into additional aromatic hydrocarbons, with said portions of said aromatic rich stream being introduced into said zon-e a temperature of less than 1600 F. and thereby controlling the resul-ting exothermiic reaction effecting the conversion of olenic hydrocarbons to aromatic hydrocarbons, withdrawing a resulting substantially aromatic hydrocarbon stream from said Zone and quench-ing it with a relatively heavy aromatic oil stream to effect the cooling and separation of resulting substantially heavy non-volatile aro matic oils, passing a resulting quenched and separated aromatic hydrocarbon stream to a fractionation zone and effecting the fractional distillation and recovery of desired substantially pure aromatic fractions.

3. The method of claim 2 further characterizedI in that said separated and quenched aromatic stream is subjected to countercurrent contact with an aromatic absorption oil prior to passing the stream` to said fractionation Zone, and said absorption oil comprises an aromatic oil boiling in the range of from about ZOO-400 F.

4. The method of claim 2 further characterized in that said heavy aromatic quenching oil contacting said resulting aromatic product stream comprises a substantially heavy aromatic oil boiling lin the range of from about 600 F, to about 800 F.

References Cited in the file of this patent UNITED STATES PATENTS 1,441,341 Govers Ian. 9, 1923 1,847,239 Frey et al. Mar. 1, 1932 2,143,014 Klein Jan. 10, 1939 2,326,799 Pier et al Aug. 17, 1943 2,416,894 Barron Mar. 14, 1947 2,431,515 Shepardson Nov. 25, 1947 2,653,175 Davis Sept. 22, 1953 

1. A METHOD FOR PRODUCING AND RECOVERING A HIGH YIELD OF AROMATIC HYDROCARBONS, WHICH COMPRISES, PASSING A NORMALLY GASEOUS PARAFFINIC HYDROCARBON STREAM INTO ADMIXTURE WITH A STREAM OF CONTROLLED OXYGEN CONTENT AND EFFECTING THE OXIDATIVE CRACKING OF SAID GASEOUS HYDROCARBON STREAM TO PROVIDE A LOW MOLECULAR WEIGHT OLEFINIC HYDROCARBONS AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 1400* F. TO ABOUT 1600E F., PASSING THE RESULTING OLEFINIC HYDROCARBON STREAM AT THE AFORESAID RESULTING TEMPERATURE INTO A CONFINED CRACKING AND AROMATIZATION ZONE AT A PRESSURE BELOW ABOUT 400 P.S.I.G. AND COMMINGLEING WITH SAID PRODUCT STREAM AN AROMATIC RICH HYDROCARBON STREAM, THE LATTER STREAM BEING INTRODUCED INTO SAID CONVERSION ZONE AND INTO ADMIXTURE WITH SAID OXIDATIVELY CRACKED STREAM IN INCREMENTAL PORTIONS ALONG THE LINE OF FLOW OF THE LATTER IN SAID ZONE, AND WITH SAID AROMATIC RICH STREAM BEING INTRODUCED INTO SAID CONVERSION ZONE AT A TEMPERATURE OF LESS THAN 1600* F. AND THEREBY CONTROLLING EXOTHERMIC AROMATICS FORMING REACTIONS TO EFFECT THE THERMAL CONVERSION OF A MAJOR PORTION OF THE NON-AROMATIC COMPONENTS OF SAID AROMATIC RICH STREAM INTO ADDITIONAL OLEFINS AND AROMATIC HYDROCARBONS WHILE SIMULTANEOUSLY CONVERTING RESULTING OLEFINIC COMPONENTS FROM SAID OXIDATIVELY CRACKED STREAM INTO ADDITIONAL AROMATIC HYDROCARBONS, WITHDRAWING A RESULTING SUBSTANTIALLY AROMATIC HYDROCARBON STREAM FROM SAID ZONE AND SUBJECTING IT TO COOLING AND FRACTIONAL DISTILLATION AND RECOVERING DESIRED SUBSTIALLY PURE AROMATIC FRACTIONS. 